Shaken confidence in Beijing’s role in market led to wild swings in recent days

China’s shares suffered their worst month in nearly six years this July, revealing not only receding confidence in Beijing’s ability to stem the selling, but also the reach of China’s troubles into other markets.

Wavering conviction that Beijing would keep its pledge to support the market drove wild intraday swings this week in the Shanghai Composite Index, which ended 1.1% lower on Friday at 3663.73. The index is down 10% for the week and 14% for July, its worst monthly performance since August 2009.